Deterioration degree estimation device and deterioration degree estimation method

ABSTRACT

A deterioration degree estimation device includes an internal resistance detection unit, a deterioration management unit and a deterioration degree estimation unit. The internal resistance detection unit detects an internal resistance of a battery. The deterioration management unit manages a cycle deterioration of the battery. The deterioration degree estimation unit estimates a deterioration degree of the battery as an estimated deterioration degree based on an increase rate of the internal resistance. The deterioration degree estimation unit estimates the estimated deterioration degree such that the estimated deterioration degree decreases as the cycle deterioration increases, or such that the estimated deterioration degree increases as the cycle deterioration degree decreases.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a U.S. National stage application of InternationalApplication No. PCT/JP2015/074021, filed Aug. 26, 2015.

BACKGROUND Field of the Invention

The present invention relates to a deterioration degree estimationdevice and a deterioration degree estimation method for estimating thedeterioration degree of a battery.

Background Information

As a method of determining the deterioration degree of a lithium ionsecondary battery, a method of detecting the deterioration degree of abattery from the internal resistance of the secondary battery is known.As a property of a battery, since the internal resistance of a batteryis increased when the battery deteriorates, the deterioration degree ofthe battery can be detected from the internal resistance. First, thevoltage and the current that flows in the battery are detected, and theinternal resistance of the battery is calculated from a predeterminedformula. A table for specifying the deterioration degree from theinternal resistance is stored. Then, the deterioration degree iscalculated using the stored table (Japanese Laid Open Patent ApplicationNo. 2008-228492-referred to as Patent Document 1).

SUMMARY

However, since, in the deterioration degree determination methoddescribed above, the deterioration degree of the battery is determinedusing only the internal resistance of the battery, there is the problemthat the estimation accuracy of the deterioration degree is low.

The problem to be solved by the present invention is to provide adeterioration degree estimation device or a deterioration degreeestimation method with a high estimation accuracy.

The present invention solves the problem described above by managing thebattery cycle deterioration, estimating an estimated deteriorationdegree of the battery based on the increase rate of the internalresistance of the battery, such that the estimated deterioration degreedecreases as the cycle deterioration increases, or such that theestimated deterioration degree increases as the cycle deteriorationdegree decreases.

According to the present invention, when the internal resistance of thebattery increases, a value corresponding to how the battery is used isreflected in the calculation of the deterioration degree; therefore, theestimation accuracy of the deterioration degree is increased.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block view of a deterioration degree estimation deviceaccording to an embodiment of the present invention.

FIG. 2 is a block view of a battery controller of FIG. 1.

FIG. 3 is a graph illustrating the characteristics of the resistanceincrease rate, the ratio of the current integration value, and thecapacity retention rate.

FIG. 4 is a block view of the battery controller in a deteriorationdegree estimation device according to another embodiment of the presentinvention.

FIG. 5 is a graph illustrating the time characteristic of the capacityretention rate and the deterioration degree.

FIG. 6 is a graph of the time characteristics illustrating therelationship between the battery temperature and the deteriorationcoefficient.

FIG. 7 is a graph of the time characteristics illustrating therelationship between the SOC and the deterioration coefficient.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Embodiments of the present invention will be explained below based onthe drawings.

First Embodiment 1

FIG. 1 is a block view of a deterioration degree estimation deviceaccording to an embodiment of the present invention. The deteriorationdegree estimation device is provided in a vehicle, and the like, thathas a battery. The deterioration degree estimation device is not limitedto a vehicle, and can be provided in another device equipped with abattery.

The deterioration degree estimation device comprises a battery 1, a load2, a current sensor 3, a voltage sensor 4, and a battery controller 10.The battery 1 is configured from a plurality of secondary batteries thatare connected in series or in parallel. The secondary battery is alithium ion battery, a nickel hydrogen battery, or the like. The battery1 is connected to a charger, which is not shown.

The load 2 is connected to the battery 1 by wiring. The load 2 is drivenby the electric power of the battery 1. The load 2 is a motor, or thelike. The current sensor 3 and the voltage sensor 4 detect the state ofthe battery, and are electrically connected to the battery 1. Thecurrent sensor 3 detects the current of the battery 1. The voltagesensor 4 detects the voltage of the battery 1. The detection values ofthe current sensor 3 and the voltage sensor 4 are output to the batterycontroller 10. The battery controller 10 is a control device formanaging the state of the battery 1.

Next, the configuration of the battery controller 10 will be describedusing FIG. 2. FIG. 2 is a block view of the battery controller 10. Thebattery controller 10 is configured from a CPU, a ROM, and the like. Thebattery controller 10 comprises a controller illustrated in FIG. 2 as afunction block for estimating the deterioration degree of the battery 1.The battery controller 10 comprises an internal resistance managementunit 20, a deterioration management unit 30, and a deterioration degreeestimation unit 40.

The internal resistance management unit 20 manages the internalresistance of the battery 1 on the basis of the detected current of thecurrent sensor 3 and the detected voltage of the voltage sensor 4. Theinternal resistance management unit 20 comprises an internal resistancedetection unit 21 and a resistance increase rate calculation unit 22.

The internal resistance detection unit 21 detects (calculates) theinternal resistance of the battery 1 on the basis of the detected valueof the current sensor 3 and the detected value of the voltage sensor 4.The resistance increase rate calculation unit 22 calculates the increaserate of the internal resistance.

The deterioration management unit 30 manages the cycle deterioration ofthe battery 1. In the present embodiment, the deterioration managementunit 30 manages the cycle deterioration degree by calculating thecurrent integration value of the battery 1. The deterioration managementunit 30 comprises an actual current integration value calculation unit31, a time management unit 32, a reference current integration valuecalculation unit 33, and an integration value ratio calculation unit 34.

The actual current integration value calculation unit 31 calculates thecurrent integration value of the battery 1 by integrating the detectedcurrent of the current sensor 3. The time management unit 32 manages theelapsed time from the start of use of the battery 1. The referencecurrent integration value calculation unit 33 calculates a referencecurrent integration value on the basis of the elapsed time that ismanaged by the time management unit 32. The current integration valuethat is calculated by the actual current integration value calculationunit 31 is the integrated value of the actual discharge current. On theother hand, the reference current integration value that is calculatedby the reference current integration value calculation unit 33 is acurrent integration value corresponding to the elapsed time, and is notan integrated value of the actual discharge current.

The integration value ratio calculation unit 34 calculates the ratio ofthe current integration value. The ratio is the actual currentintegration value relative to the reference current integration value.

The deterioration degree estimation unit 40 calculates the deteriorationdegree of the battery 1 on the basis of the internal resistance of thebattery 1. In addition, the deterioration degree estimation unit 40corrects the deterioration degree corresponding to the internalresistance, in accordance with the magnitude of the current integrationvalue ratio that is calculated by the integration value ratiocalculation unit 34. The deterioration degree estimation unit 40 therebyestimates the corrected deterioration degree as the final deteriorationdegree of the battery 1.

Next, the method of estimating the deterioration degree of the battery 1will be described with reference to FIG. 2 and FIG. 3. FIG. 3 is a graphillustrating the correspondence between the resistance increase rate,the ratio of the current integration value, and the capacity retentionrate. Steps S1-S7 of the block view of FIG. 2 illustrate the controlflow of the deterioration degree estimation method.

The internal resistance detection unit 21 uses a current sensor 3 and avoltage sensor 4 to acquire the detected current and the detectedvoltage, plots the acquired detected current and detected voltage on agraph having the current value and the voltage value as axes, and, atthe same time, calculates the IV characteristic, which is a straightline approximating the plotted current value and voltage value, andcalculates the internal resistance from the inclination of the IVcharacteristic (Step S1). The method of calculating the internalresistance is not limited to the method of calculating from theinclination oxide film layer the IV characteristic, and can be anothermethod. For example, the internal resistance can be calculated bysubstituting the current value detected by the current sensor 3 and thevoltage value detected by the voltage sensor 4 into a battery modelformula, which is stored in advance and which includes the currentvalue, voltage value, and internal resistance in the parameter. Sincethese internal resistance calculation methods are well-known, thedetails are not described herein.

The resistance increase rate calculation unit 22 calculates theresistance increase rate by calculating the ratio of the initial valueof the internal resistance (the internal resistance value correspondingto the internal resistance value when the battery 1 is new, and which isstored in advance), and the internal resistance calculated by theinternal resistance detection unit 21 (Step S2). The increase rate ofthe internal resistance corresponds to the ratio of the calculated valueof the internal resistance relative to the initial value of the internalresistance. That is, the resistance increase rate means the increaserate relative to the initial value of the internal resistance. Theinitial value of the internal resistance can be a value stored inadvance in the resistance increase rate calculation unit 22.Alternatively, the initial value can be a value calculated by theinternal resistance detection unit 21 at the time of start of use of thebattery 1. The resistance increase rate calculation unit 22 outputs thecalculated resistance increase rate to the deterioration degreeestimation unit 40.

The actual current integration value calculation unit 31 calculates theactual current integration value of the battery 1 by integrating thedetected current of the current sensor 3 (Step S3). The currentintegration value is the integrated value of the discharge current ofthe battery 1. In addition, the current integration value is the currentintegration value from the start of use of the battery 1 to the present.The time management unit 32 manages the elapsed time of the battery 1,in accordance with the calculation timing of the current integrationvalue by the actual current integration value calculation unit 31 (StepS4).

The reference current integration value calculation unit 33 calculatesthe current integration value corresponding to the elapsed time as thereference current integration value (Step S5). The reference currentintegration value is a value in which the current integration value atthe elapsed time is set in advance. The reference current integrationvalue is a value that is set in advance as an evaluation value thatevaluates the integrated value of the discharge current under a PRenvironment. The reference current integration value becomes larger asthe elapsed time increases. For example, if 1 C charging and 1 Cdischarging are repeated for a predetermined number of times during apredetermined period, the integrated value of the discharge time duringthe predetermined period becomes the reference current integration valuecorresponding to said predetermined period. The correspondencerelationship between the elapsed time and the reference currentintegration value is stored in the reference current integration valuecalculation unit 33 in advance as a map, or the like.

The integration value ratio calculation unit 34 calculates the ratio ofthe current integration value (Step S6). The ratio of the currentintegration value is the ratio of the actual current integration valueat a predetermined elapsed time and the reference current integrationvalue corresponding to said elapsed time. If the ratio of the currentintegration value is high, the actual current integration value becomeslarge; therefore, the cycle deterioration becomes larger than thestorage deterioration. On the other hand, if the ratio of the currentintegration value is low, the actual current integration value becomessmall relative to the current integration value that was evaluatedbeforehand (corresponding to the reference current integration value);therefore, the cycle deterioration becomes smaller than the storagedeterioration. That is, the ratio of the current integration valuerepresents the rate of the influence of cycle deterioration at theelapsed time. Here, in general, storage deterioration is deteriorationthat occurs over time regardless of the charging and discharging of thebattery, and cycle deterioration means deterioration that occurs due tothe charging and discharging of the battery.

Meanwhile, as a characteristic of the battery 1, the internal resistanceincreases as the deterioration of the battery 1 progresses. Accordingly,it is possible to calculate the deterioration degree of the battery 1from the increase rate of the internal resistance. The deteriorationdegree of the battery 1 is represented by the storage deterioration andthe cycle deterioration. That is, the deterioration of the battery 1includes storage deterioration and cycle deterioration. From the pointof view of influence on the deterioration degree, even if thedeterioration degree of the battery 1 is the same value (the increaserate of the internal resistance is the same), the rate at which thestorage deterioration influences the deterioration degree and the rateat which the cycle deterioration influences the deterioration degree aredifferent depending on how the battery is used.

Here, it is assumed that a predetermined period has elapsed since thestart of use of the battery 1, and that the increase rate of theinternal resistance has reached a predetermined value. If the cycledeterioration has a greater influence on the deterioration degree of thebattery 1 than the storage deterioration when the increase rate of theinternal resistance reaches the predetermined value, the deteriorationspeed of the battery 1 is high, and the elapsed time from the start ofuse becomes short. On the other hand, if the storage deterioration has agreater influence on the deterioration degree of the battery 1 than thecycle deterioration when the increase rate of the internal resistancereaches the predetermined value, the deterioration speed of the battery1 is low, and the elapsed time from the start of use becomes long. Thedeterioration degree of the battery 1 is larger when the increase rateof the internal resistance reaches the predetermined value over a longtime. That is, if the increase rate of the internal resistance is thesame, the deterioration degree of the battery 1 decreases as the cycledeterioration increases, and the deterioration degree of the battery 1increases as the storage deterioration increases. The deteriorationdegree estimation unit 40 estimates the deterioration degree of thebattery 1 using this characteristic.

The deterioration degree estimation unit 40 stores the correspondencerelationship between the resistance increase rate, the ratio of thecurrent integration value, and the capacity retention rate as a map.According to the correspondence relationship represented by the map, thecapacity retention rate decreases as the resistance increase rateincreases, as illustrated in FIG. 3. In addition, when the resistanceincrease rate is set to a constant value, the capacity retention ratedecreases as the ratio of the current integration value decreases. Inother words, it can be said that if the deterioration degree of thebattery is constant, the capacity retention rate decreases as the ratioof the cycle deterioration decreases, that is, as the ratio of thestorage deterioration increases. Furthermore, it can also be said thatif the deterioration degree of the battery is constant, the capacityretention rate increases as the ratio of the cycle deteriorationincreases, that is, as the ratio of the storage deterioration decreases.The capacity retention rate is in an inverse relationship with thedeterioration degree of the battery 1, and the deterioration degreedecreases as the capacity retention rate increases. The deteriorationdegree estimation unit 40 refers to a map, and estimates the capacityretention rate corresponding to the resistance increase rate and theratio of the current integration value as the current capacity retentionrate of the battery 1 (Step S7). When the resistance increase rate isthe same value, the deterioration degree estimation unit 40 estimatesthe current deterioration degree of the battery 1 such that thedeterioration degree of the battery 1 decreases as the ratio of thecurrent integration value increases. As a result, the deteriorationdegree estimation unit 40 corrects the resistance deterioration degreecalculated based on the internal resistance of the battery 1 such thatthe resistance deterioration degree decreases as the cycle deteriorationincreases, and estimates the corrected resistance deterioration degreeas the current deterioration.

As described above, in the present embodiment, the internal resistanceof the battery 1 is calculated, the cycle deterioration of the battery 1is managed, and the deterioration degree of the battery 1 is estimatedbased on the increase rate of the internal resistance of the battery 1.Then, the estimated deterioration degree of the battery 1 is decreasedas the cycle deterioration is increased. It is thereby possible toincrease the estimation accuracy of the deterioration degree of thebattery 1.

In addition, in the present embodiment, the cycle deterioration ismanaged by calculating the current integration value of the battery 1.It is thereby possible to easily grasp how the battery 1 is used.

In addition, in the present embodiment, a map representing thecorrespondence relationship between the increase rate of the internalresistance, the current integration value, and the deterioration degreeis stored in advance, and the deterioration degree is estimated withreference to the map. Since it is thereby possible to grasp thetransition of the deterioration degree according to how the battery isused in accordance with the battery characteristics, it is possible toincrease the estimation accuracy of the deterioration degree of thebattery 1.

As a modified example of the present embodiment, the deteriorationdegree estimation unit 40 can calculate a deterioration degreecorresponding to the increase rate of the internal resistance, correctthe calculated deterioration degree based on the current integrationvalue, and estimate the corrected deterioration degree as thedeterioration degree of the battery 1. A map representing thecorrespondence relationship between the increase rate of the internalresistance and the deterioration degree is stored in advance in thedeterioration degree estimation unit 40. A correction coefficient forcorrecting the deterioration degree is set in advance in thedeterioration degree estimation unit 40. The correction coefficientchanges according to the current integration value. The maximum value ofthe correction coefficient is set to 1.0, and the correction coefficientdecreases as the ratio of the current integration value decreases. Then,the deterioration degree estimation unit 40 estimates the finaldeterioration degree by multiplying the deterioration degree calculatedfrom the map by the correction coefficient. As a result, when theinternal resistance of the battery 1 reaches a certain internalresistance, the estimated deterioration degree decreases as the cycledeterioration increases. The setting value of the correction coefficientcan be a value other than 1.0, and the calculation method for correctingthe deterioration degree can be another method.

In addition, as a modified example of the present embodiment, thedeterioration degree estimation unit 40 can correct the increase rate ofthe internal resistance based on the current integration value. A maprepresenting the correspondence relationship between the increase rateof the internal resistance and the deterioration degree is stored inadvance in the deterioration degree estimation unit 40. In addition, acorrection coefficient for correcting the increase rate of the internalresistance is set in advance in the deterioration degree estimation unit40. The correction coefficient changes according to the currentintegration value. The maximum value of the correction coefficient isset to 1.0, and the correction coefficient increases as the ratio of thecurrent integration value decreases. The deterioration degree estimationunit 40 calculates the corrected internal resistance increase rate bymultiplying the increase rate of the internal resistance by thecorrection coefficient. The corrected internal resistance increase rateincreases as the ratio of the current integration value decreases. Then,the deterioration degree estimation unit 40 refers to the map, andestimates the deterioration degree corresponding to the correctedinternal resistance increase rate as the final deterioration degree.

In addition, as a modified example of the present embodiment, thedeterioration degree estimation unit 40 can correct the deteriorationdegree based on the temperature of the battery 1. The deteriorationdegree of the battery 1 has a dependency with respect to thetemperature, and the degree of progress of deterioration differsdepending on the temperature of the battery 1. The battery 1 has acharacteristic of being easily deteriorated at a certain temperature andnot being easily deteriorated at other temperatures. The deteriorationdegree estimation unit 40 stores a correction coefficient thatrepresents the relationship between deterioration and temperature, andcarries out a correction based on the temperature by multiplying theestimated deterioration degree by the correction coefficient. As aresult, it is possible to increase the estimation accuracy of thedeterioration degree. In addition to a method of multiplying acorrection coefficient, the method of correcting the deteriorationdegree can be a calculation method that uses a map. The temperature ofthe battery 1 can be detected by a sensor provided to the battery 1.

In addition, as a modified example of the present embodiment, thedeterioration degree estimation unit 40 can correct the deteriorationdegree based on the charging state of the battery 1 (SOC: State ofCharge). The deterioration degree of the battery 1 has a dependency withrespect to the SOC, and the degree of progress of deterioration differsdepending on the SOC of the battery 1 (the SOC when the battery 1 isstored, the SOC when the battery 1 is used). The battery 1 has acharacteristic of being easily deteriorated at a certain SOC and notbeing easily deteriorated at other SOCs. The deterioration degreeestimation unit 40 stores a correction coefficient that represents therelationship between SOC and temperature//I think this should be“relationship between SOC and deterioration degree”//, and carries out acorrection based on the SOC by multiplying the estimated deteriorationdegree by the correction coefficient. As a result, it is possible toincrease the estimation accuracy of the deterioration degree. Inaddition to a method of multiplying a correction coefficient, the methodof correcting the deterioration degree can be a calculation method thatuses a map. The SOC of the battery 1 can be obtained by calculationusing the detection value of the current sensor 3 or the detection valueof the voltage sensor 4.

Second Embodiment

A deterioration degree estimation device according to another embodimentof the present invention will be described using FIG. 4. The presentembodiment is different from the first embodiment described above in thepoint that the storage deterioration of the battery 1 is managed, andthe deterioration degree of the battery 1 is estimated in accordancewith the magnitude of the storage deterioration. The otherconfigurations are the same as the above-described first embodiment, andthe descriptions thereof are incorporated by reference. FIG. 4 is ablock view of the battery controller 10.

The battery controller 10 comprises an internal resistance managementunit 20, a deterioration degree estimation unit 40, and a storagedeterioration management unit 50. The configuration of the internalresistance management unit 20 is the same as the configuration of theinternal resistance management unit 20 according to the firstembodiment.

The storage deterioration management unit 50 manages the storagedeterioration of the battery 1. In the present embodiment, the storagedeterioration management unit 50 manages the storage deterioration ofthe battery 1 by measuring the elapsed time of the battery 1 using atimer. Storage deterioration is deterioration that progresses over timedue to a chemical reaction between the electrolyte and the electrode ofa battery. The storage deterioration management unit 50 measures theelapsed time since the electrode comes in contact with the electrolyte,and obtains the current storage deterioration based on the elapsed time.

The storage deterioration managed by the storage deteriorationmanagement unit 50 is set as the storage deterioration from when theelectrode comes in contact with the electrolyte to the present time. Thestorage deterioration management unit 50 measures the time from when theelectrode comes in contact with the electrolyte to the present time asthe elapsed time, and calculates the storage deterioration based on theelapsed time.

The characteristic of the storage deterioration is illustrated in FIG.5. FIG. 5 is a graph illustrating the time characteristic of the storagedeterioration. In FIG. 5, the horizontal axis represents the square rootof time, and the vertical axis represents the deterioration degree ofthe storage deterioration and the capacity retention rate. Thecharacteristic illustrated in FIG. 5 can be acquired using a commonstorage test for battery evaluation.

Storage deterioration progresses in proportion to the square root oftime, as illustrated in FIG. 5. A map representing the relationshipbetween elapsed time and storage deterioration is stored in the storagedeterioration management unit 50. The storage deterioration managementunit 50 calculates the deterioration degree corresponding to the elapsedtime as the storage deterioration with reference to this map.

The deterioration degree estimation unit 40 stores the correspondencerelationship between the resistance increase rate, the storagedeterioration degree, and the capacity retention rate as a map.According to the correspondence relationship represented by the map, thecapacity retention rate decreases as the resistance increase rateincreases. In addition, when the resistance increase rate is set to aconstant value, the capacity retention rate decreases as the storagedeterioration degree increases. The deterioration degree estimation unit40 refers to a map, and estimates the capacity retention ratecorresponding to the resistance increase rate and the storagedeterioration degree as the current capacity retention rate of thebattery 1. When the resistance increase rate is the same value, thedeterioration degree estimation unit 40 estimates the currentdeterioration degree of the battery 1 such that the deterioration degreeof the battery 1 increases as the ratio of the storage deteriorationdegree increases. As a result, the deterioration degree estimation unit40 corrects the resistance deterioration degree calculated based on theinternal resistance of the battery 1 such that the resistancedeterioration degree increases as the storage deterioration increases,and estimates the corrected resistance deterioration degree as thecurrent deterioration.

As described above, in the present embodiment, the internal resistanceof the battery 1 is calculated, the storage deterioration of the battery1 is managed, and the deterioration degree of the battery 1 is estimatedbased on the increase rate of the internal resistance of the battery 1.Then, the estimated deterioration degree of the battery 1 is increasedas the storage deterioration is increased. It is thereby possible toincrease the estimation accuracy of the deterioration degree of thebattery 1.

Since the storage deterioration management unit 50 measures time using atimer mounted in a vehicle, the time from when the electrode comes incontact with the electrolyte to when timing with the vehicle timer isstarted in the battery manufacturing process cannot be timed. Therefore,the time from when the electrode comes in contact with the electrolyteto when timing with the vehicle timer is started can be managed to be afixed time, and the fixed time can be added to the time measured by thetimer. In addition, since the time from when the electrode comes incontact with the electrolyte to when timing with the vehicle timer isstarted is extremely short compared to the life of the battery 1, thetime can simply be ignored.

In addition, as a modified example of the present embodiment, thestorage deterioration management unit 50 can correct the storagedeterioration based on the temperature of the battery 1. As acharacteristic of the battery 1, storage deterioration has temperaturedependence, as illustrated in FIG. 6.

FIG. 6 is a graph illustrating the time characteristics of thedeterioration coefficient. In FIG. 6, the horizontal axis represents thesquare root of time, and the vertical axis represents the deteriorationcoefficient. The deterioration coefficient is a coefficient that ismultiplied by the capacity retention rate. The capacity retention ratebecomes smaller and the deterioration degree increases as thedeterioration coefficient becomes smaller. In addition, if the time isthe same, the deterioration coefficient becomes smaller as thetemperature increases. The storage deterioration management unit 50stores in advance a correction coefficient that represents therelationship between storage deterioration and temperature. Thiscorrection coefficient corresponds to the deterioration coefficient.However, while the deterioration coefficient shown by the characteristicof FIG. 6 is a coefficient that is multiplied by the capacity retentionrate, the correction coefficient is set to a coefficient that cancalculate the deterioration degree while maintaining the relationshipshown by the characteristic of FIG. 6.

The storage deterioration management unit 50 uses temperatureinformation that is output by the temperature sensor of the battery 1and stores, in a memory, the frequency of the temperature up to thistime at a set period unit, based on the time information of the timer.The storage deterioration management unit 50 corrects the storagedeterioration degree using the temperature information stored in thememory. Specifically, for example, the storage deterioration managementunit 50 obtains the time that the battery 1 is exposed to thetemperature, using temperature occurrence frequency information that isstored. Next, the storage deterioration management unit 50 calculatesthe storage deterioration degree with respect to the obtained time, andmultiplies the storage deterioration degree by the correctioncoefficient. The storage deterioration management unit 50 carries outthe same calculation for each temperature interval, and calculates thestorage deterioration degree for each interval. Then, the storagedeterioration management unit 50 calculates the final storagedeterioration degree by calculating the storage deterioration degree foreach interval. The storage deterioration management unit 50 therebycorrects the storage deterioration based on the temperature of thebattery 1. In the present embodiment, it is possible to increase thecalculation accuracy of the storage deterioration degree by applyingtemperature sensitivity to the storage deterioration of the battery 1.

In addition, as a modified example of the present embodiment, thestorage deterioration management unit 50 can correct the storagedeterioration based on the SOC of the battery 1. As a characteristic ofthe battery 1, storage deterioration is dependent on the SOC, asillustrated in FIG. 7.

FIG. 7 is a graph illustrating the time characteristics of thedeterioration coefficient. In FIG. 7, the horizontal axis represents thesquare root of time, and the vertical axis represents the deteriorationcoefficient. The deterioration coefficient is the same as thedeterioration coefficient shown in FIG. 6. The capacity retention ratebecomes smaller and the deterioration degree increases as thedeterioration coefficient becomes smaller. In addition, if the time isthe same, the deterioration coefficient becomes smaller as the SOCincreases.

The storage deterioration management unit 50 stores in advance acorrection coefficient that represents the relationship between storagedeterioration and SOC. The storage deterioration management unit 50 usesthe SOC, and stores, in a memory, the frequency of the SOC up to thistime at a set period unit, based on the time information of the timer.The storage deterioration management unit 50 corrects the storagedeterioration degree using the SOC information stored in the memory.Specifically, for example, the storage deterioration management unit 50obtains the time that the battery 1 maintains the SOC, using the SOCoccurrence frequency information that is stored. Next, the storagedeterioration management unit 50 calculates the storage deteriorationdegree with respect to the obtained time, and multiplies the storagedeterioration degree by the correction coefficient. The storagedeterioration management unit 50 carries out the same calculation foreach SOC interval, and calculates the storage deterioration degree foreach interval. Then, the storage deterioration management unit 50calculates the final storage deterioration degree by calculating thestorage deterioration degree for each interval. The storagedeterioration management unit 50 thereby corrects the storagedeterioration based on the SOC of the battery 1. In the presentembodiment, it is possible to increase the calculation accuracy of thestorage deterioration degree by applying the SOC sensitivity to thestorage deterioration of the battery 1.

The storage deterioration management unit 50 can correct the storagedeterioration degree based on the temperature and the SOC of the battery1 by combining the two modified examples described above.

The storage deterioration management unit 50 described above correspondsto the deterioration management unit of the present invention.

The invention claimed is:
 1. A capacity retention rate estimation devicecomprising: a controller configured to: detect an internal resistance ofa battery; determine a rate of increase of the internal resistance ofthe battery, the rate of increase of the internal resistance being arate at which the internal resistance of the battery increases withrespect to an initially detected internal resistance of the battery;calculate an actual current integration value by integrating a detecteddischarge current of the battery during an elapsed time from a start ofbattery use to a present time and calculate a reference currentintegration value based on the elapsed time; calculate an integratedcurrent ratio, which is a ratio of the actual current integration valueto the reference current integrated value; and estimate a capacityretention rate of the battery as an estimated capacity retention ratebased on a map that shows a correspondence relationship between thedetermined rate of increase of the internal resistance and theintegrated current ratio, the map showing that: the capacity retentionrate decreases as the rate of increase of the internal resistanceincreases, and the capacity retention rate decreases as the integratedcurrent ratio decreases.
 2. The capacity retention rate estimationdevice according to claim 1, wherein the controller is configured tocorrect the determined rate of increase of the internal resistance basedon the actual current integration value.
 3. The capacity retention rateestimation device according to claim 1, wherein the controller isconfigured to calculate the capacity retention rate of the batterycorresponding to the determined rate of increase of the internalresistance as a reference capacity retention rate, correct the referencecapacity retention rate based on the actual current integration valueand estimate a corrected reference capacity retention rate as theestimated capacity retention rate.
 4. The capacity retention rateestimation device according to claim 1, wherein the controller isconfigured to correct the estimated capacity retention rate based on atemperature of the battery.
 5. The capacity retention rate estimationdevice according to claim 1, wherein the controller is configured tocorrect the estimated capacity retention rate based on a charging stateof the battery.
 6. A capacity retention rate estimation methodcomprising: detecting an internal resistance of a battery; determining arate of increase of the internal resistance of the battery, the rate ofincrease of the internal resistance being a rate at which the internalresistance of the battery increases with respect to an initiallydetected internal resistance of the battery; calculating an actualcurrent integration value by integrating a detected discharge current ofthe battery during an elapsed time from a start of battery use to apresent time and calculate a reference current integration value basedon the elapsed time; calculating an integrated current ratio, which is aratio of the actual current integration value to the reference currentintegrated value; and estimating a capacity retention rate of thebattery as an estimated capacity retention rate based on a map thatshows a correspondence relationship between the determined rate ofincrease of the internal resistance and the integrated current ratio,the map showing that: the capacity retention rate decreases as the rateof increase of the internal resistance increases, and the capacityretention rate decreases as the integrated current ratio decreases.